This invention concerns a circuit arrangement for ignition and operation of a high pressure gas discharge lamp in motor vehicles of a type including a DC/AC converter which is connected via a resonance ignition device to the high pressure gas discharge lamp, a power regulating device which has a current measuring device in series with the high pressure gas discharge lamp, a voltage measuring device in parallel with the high pressure gas discharge lamp, and a multiplier whose inputs are coupled with the voltage measuring device and the current measuring device and whose output is coupled to the DC/AC converter, a phase regulating loop including a phase comparator whose output is coupled with a voltage control oscillator which controls the DC/AC converter, wherein a first input of the phase comparator is coupled with the voltage measuring device and the second input of the phase comparator is coupled with a junction between the voltage control oscillator and the resonance ignition device.
An apparatus for ignition and operation of an electrical gas discharge lamp is disclosed in German Patent Application P 38 43 029 which includes a DC/AC converter which is coupled to the high pressure gas discharge lamp via a superimposed ignition device. The apparatus includes a power regulating device which comprises a current measuring device in series with the high pressure gas discharge lamp, a voltage measuring device in parallel with the high pressure gas discharge lamp and a multiplier. The multiplier multiples a voltage signal from the voltage measuring device with a voltage signal from the current measuring device and forms a power value which, in this manner, controls the DC/AC converter via the output of the multiplier so that power of voltage produced by the DC/AC converter is regulated. The apparatus includes additionally a phase regulating loop which is constructed as a phase lock loop (PLL) and which includes a phase comparator whose output is coupled with a voltage controlled oscillator which, in turn, controls the DC/AC converter. The first input of the phase comparator is in this device coupled with the voltage measuring device while the second input of the phase comparator is coupled with a junction of the voltage control oscillator and the superimposed ignition device. This known apparatus thereby makes possible, for one thing, the regulation of power to the high pressure gas discharge lamp and, for another thing, regulation of the phase and frequency of operation voltage from the DC/AC converter through the phase regulating loop.
A circuit arrangement for operation of a discharge lamp from a small-volt DC voltage source is known from European Patent Application 0 294 604 A1 in which a DC/AC converter is coupled via a resonance ignition loop with a high pressure gas discharge lamp. The circuit arrangement includes additionally a power regulating device which regulates the frequency of alternating voltage developed by the DC/AC converter in dependence, or as a function of, voltage measured in a lamp circuit which relates to regulation of power of the high pressure gas discharge lamp. The DC/AC converter requires in this device an additional transformer for the control of a semiconductor switching device.
It is disadvantageous that in some known circuits a large number of power transistors are required for the DC/AC converter and in addition an additional transformer is necessary for controlling the power transistors. Further, it has proven to be disadvantageous that in order to influence frequency of alternating voltage from the DC/AC converter an additional power transistor is necessary whereby, overall, a cost intensive embodiment results.
It is an object of this invention to provide a circuit arrangement for ignition and operation of a high pressure gas discharge tube which is uncomplicated and cost effective and, in addition to providing best possible ignition of the high pressure gas discharge lamp, also makes possible power regulation of the high pressure discharge lamp.